@InProceedings{DoyleBarr:2006:ReENPh,
author = "Doyle, Moira and Barros, Vicente",
affiliation = "Departamento de Ciencias de la Atm{\'o}sfera y los
Oc{\'e}anos,UBA, CIMA-CONICET, Ciudad Universitaria,
Pabell{\'o}n II, 2do piso, 1428, Buenos Aires, Argentina",
title = "Precipitation trends in southeastern South America: relationship
with ENSO phases",
booktitle = "Proceedings...",
year = "2006",
editor = "Vera, Carolina and Nobre, Carlos",
pages = "1513--1517",
organization = "International Conference on Southern Hemisphere Meteorology and
Oceanography, 8. (ICSHMO).",
publisher = "American Meteorological Society (AMS)",
address = "45 Beacon Hill Road, Boston, MA, USA",
keywords = "trend, precipitation, ENSO, South America.",
abstract = "During the second half of the twentieth century, in subtropical
South America to the east of the Andes, rainfall trends were
observed in precipitation series from local networks. The
relationship of these trends with the different phases of El
Niño-Southern Oscillation (ENSO) is explored in this paper. As
precipitation changes are characterized by linear trends, under
certain conditions, the total linear trend is the result of adding
the partial linear trends corresponding to each of the ENSO
phases, i.e. El Niño, La Niña and Neutral events. When splitting a
series in various sub series, the linear trends of these sub
series add up to the same value as the linear trend of the entire
series if each of the sub series has its elements ordered in time
around the same mean value and variance as the complete series. A
linear trend is a special case of a linear regression slope when
the independent variable is time. These conditions were
approximately fulfilled during the period 1960-1999. This property
permits to isolate the linear trends of any variable corresponding
to each phase, and therefore, helps to highlight or discard any
possible relationship between the linear trends of the variables
and the ENSO phases. Annual rainfall linear trends were calculated
applying a linear regression model, to each grid point of a 3ºx3º
mesh between 70º 40ºW and 16º 40ºS; regression coefficients were
tested for significance through a t-test. There are positive
linear trends south of 22ºS and negative to the north. In the
southern area, positive significant trends of 4mm/year or more can
be observed, i.e. an increase in precipitation exceeding 160mm in
the last 4 decades of the twenty century, which is about 30% of
the initial value. These annual rainfall trends took place
predominantly during the neutral phase of the ENSO. Significant
values extend northward from its southern nucleus along the east
side of Andes Mountains where the climate is considerably dry. In
northeastern Argentina, southern Brazil and Paraguay, half of the
annual rainfall trend was also positive and came from El Niño
phase with a minor contribution from La Niña and the neutral
phases. Indeed, in this region more than a trend there was a
change in mean value after 1980, well in phase with similar
changes in the ENSO indexes. On the other hand, the region of the
South Atlantic Convective Zone (SACZ) has a negative trend of up
to 4mm/year, which in a total of 40 years adds to almost 160mm
decrease in rainfall. Here the contribution of the neutral phase
predominates, but only in the core of the negative trends Almost
everywhere in the region, no trends or very small ones took place
during La Niña periods. Hence, in most of subtropical South
America, east of the Andes, precipitation trends during the
extreme phases of the ENSO constitute only a small part of the
trends of the last 40 years of the twentieth century.",
conference-location = "Foz do Igua{\c{c}}u",
conference-year = "24-28 Apr. 2006",
language = "en",
organisation = "American Meteorological Society (AMS)",
ibi = "cptec.inpe.br/adm_conf/2005/09.14.17.25",
url = "http://urlib.net/ibi/cptec.inpe.br/adm_conf/2005/09.14.17.25",
targetfile = "1513-1518.pdf",
type = "Understanding long-term climate variations in the SH",
urlaccessdate = "15 jun. 2024"
}